1. Field of the Invention
The present invention relates to a water quality analyzer, and in particular, to a total nitrogen measuring device for measuring the total nitrogen concentration in a liquid sample.
2. Description of Related Art
As for the method for measuring the total nitrogen where the total amount of total nitrogen compounds in a liquid sample such as industrial wastewater is represented by the concentration of nitrogen, the “ultraviolet spectrophotometric method” (JIS K 0102 45.2) that is prescribed in the “testing methods for industrial wastewater” according to the Japanese Industrial Standard is generally used. According to the ultraviolet spectrophotometric method, a liquid sample to which potassium peroxydisulfate, which is an oxidizing agent, is added is processed through autoclaving, that is to say, at a high temperature and under high pressure.
In addition, a total nitrogen measuring device is commercially available where a method gained by combining “UV photo-oxidation decomposition” with the “ultraviolet spectrophotometric method” (hereinafter, referred to as “UV photo-oxidation decomposition method”) is adopted.
In accordance with the UV photo-oxidation decomposition method, a predetermined amount (a) of a liquid sample S that has been collected is first weighed and diluted with a predetermined amount (b) of diluent water. Then, as a pre-process for alkalizing the liquid sample S so that the nitrogen compounds in the liquid sample S can be easily decomposed, a predetermined amount (c) of a sodium hydroxide solution (NaOH) is added. Next, a predetermined amount (d) of a potassium peroxydisulfate solution, which becomes an oxidizing agent, is added, and after that, a predetermined amount (a+b+c+d) of the prepared liquid sample S1 is transferred to the UV photo-oxidation decomposition process.
Next, the prepared liquid sample S1 is irradiated with ultraviolet rays under the conditions of being heated at 70 degrees or higher so as to be converted to a reacted liquid sample S2 where the nitrogen compounds in the prepared liquid sample S1 has reacted with the ultraviolet rays and oxidatively decomposed to nitrate ions. After that, a predetermined amount (e) of hydrochloric acid or the like for adjusting the pH is added at the time when the absorbance is determined, and thus, the total nitrogen concentration in a predetermined amount (a+b+c+d+e) of the prepared liquid sample S3 is measured through the determination of absorbance in the vicinity of 220 nm (see Patent Literature 1).
FIG. 4 is a diagram schematically showing an example of the entire configuration of a conventional online total nitrogen measuring device. FIG. 2 is a cross-sectional diagram showing an example of the configuration of a reactor, and FIG. 3 is a cross-sectional diagram showing an example of the configuration of a measuring unit. Here, one direction that is horizontal relative to the ground is direction X, the direction that is horizontal relative to the ground and perpendicular to the direction X is direction Y, and the direction that is perpendicular to the direction X and direction Y is direction Z.
An online total nitrogen measuring device 101 is provided with a sample tank 2, a syringe pump (weighing unit) 12, a first multiport valve 20, a second multiport valve 30, a reactor 40, a measuring unit 50 and a computer 160.
A liquid sample S such as industrial wastewater or environmental water is continuously supplied to the sample tank 2, which is connected to one distribution port of the first multiport valve 20.
The syringe pump 12 is provided with a syringe 12a having a cylindrical body, a piston 12b in columnar form that is inserted into the syringe 12a and a pulse motor 12c that is controlled by the computer 160. Thus, the piston 12b of the syringe pump 12 is moved upwards and downwards by the pulse motor 12c. When the piston 12b is drawn downwards, a predetermined amount of solution is injected into the syringe 12a, and when the piston 12b is pushed upwards, the predetermined amount of solution within the syringe 12a is discharged.
The first multiport valve 20 is made up of eight distribution ports and one common port. The sample tank 2, a container 3 containing Span liquid, a container 4 containing a standard liquid sample, a container 5 containing diluent water, the reactor 40 and the measuring unit 50 are connected to the distribution ports. In addition, the first multiport valve 20 is driven by a motor (not shown) so as to connect the common port to one selected distribution port.
The second multiport valve 30 is made of eight distribution ports and one common port. A container 6 containing a potassium peroxydisulfate solution, a container 7 containing a sodium hydroxide solution, a container 8 containing hydrochloric acid, a container 9 containing molybdic acid, a container 10 containing ascorbic acid, a container 11 containing sulfuric acid, and the common port of the first multiport valve 20 are connected to the distribution ports. Furthermore, the syringe pump 12 is connected to the common port of the second multiport valve 30. In addition, the second multiport valve 30 is driven by a motor (not shown) so as to connect the common port to one selected distribution port.
As shown in FIG. 2, the reactor 40 is provided with a reaction container 41 for containing a prepared liquid sample S1, an ultraviolet ray lamp 42 for irradiating the prepared liquid sample S1 with ultraviolet rays, and a heater 43 for controlling the temperature for oxidation reaction of the prepared liquid sample S1.
The reaction container 41 is made of a sidewall 41a in a cylindrical form (outer diameter: 12 mm, inner diameter: 10 mm, height: 130 mm, for example), and a circular bottom 41b, where a liquid sample introduction port 41c that is connected to the first multiport valve 20 is created in the lower portion of the sidewall 41a, and a liquid sample discharge port 41d that is connected to the drain for disposing of liquid waste is created on the bottom 41b. Here, the reaction container 41 is formed of crystal glass or the like.
The heater 43 is provided with a cylindrical block body made of a metal and a thermocouple (not shown) that is buried in the block body and is arranged so as to make contact with the outer peripheral surface of the reaction container 41.
The ultraviolet ray lamp 42 is a low pressure mercury lamp, an excimer lamp, a deuterium lamp, a xenon lamp or an Hg—Zn—Pb lamp, for example.
The ultraviolet ray lamp 42 is inserted from the top so as to be arranged in the center portion within the reaction container 41. As a result, when a predetermined amount of the prepared liquid sample S1 is contained within the reaction container 41, the ultraviolet ray lamp 42 is immersed in the prepared liquid sample S1.
As shown in FIG. 3, the measuring unit 50 is provided with a semiconductor laser element (light source unit) 51 for emitting a laser beam to the right (direction X), a photodiode (detection unit) 52 for detecting the light intensity I of the laser beam that progresses in the direction X, and a measuring cell (sample container) 53 for containing a predetermined amount of the prepared liquid sample S3 that is arranged between the semiconductor laser element 51 and the photodiode 52. Here, the light source unit may not necessarily be a semiconductor laser element, but may be a xenon flash lamp or the like.
The measuring cell 53 is made of a sidewall 53a in cylindrical form (outer diameter: 12 mm, inner diameter: 10 mm, height: 130 mm, for example), a circular top 53b and a circular bottom 53c, where a liquid sample discharge port 53d that is connected to the drain for disposing liquid waste is created in the top 53b, and a liquid sample introduction port 53e that is connected to the first multiport valve 20 is created on the bottom 53c. Here, the measuring cell 53 is formed of crystal glass or the like.
As a result, the laser beam that has emitted from the semiconductor laser element 51 passes through the sidewall 53a, passes through a region to be measured (light path), passes through the sidewall 53a on the opposite side, and after that is received by the photodiode 52. At this time, the laser beam is partially absorbed by a prepared liquid sample S3 in the case where the prepared liquid sample S3 is in the region to be measured.
Here, a method for automatically analyzing the total nitrogen concentration of a liquid sample S by using the above-described online total nitrogen measuring device 101 is described. The computer 160 outputs a drive signal to the pulse motor 12c in accordance with a predetermined timing, and thereby a predetermined amount (a) of a liquid sample S is weighed and collected from the sample tank 2 by the syringe pump 12. A drive signal is again outputted to the pulse motor 12c, and thereby a predetermined amount (b) of diluent water is weighed and collected from the container 5 by the syringe pump 12 so that the liquid sample S is diluted within the syringe 12a. Next, the computer 160 outputs a drive signal to the pulse motor 12c, and thereby a predetermined amount (c) of a potassium hydroxide solution in the container 7 and a predetermined amount (d) of a potassium peroxydisulfate solution in the container 6 are added to the syringe 12a so as to provide a prepared liquid sample S1. After that, a drive signal is again outputted to the pulse motor 12c, and thereby a predetermined amount (a+b+c+d) of the prepared liquid sample S1 is introduced from the syringe pump 12 to the reactor 40.
In the reactor 40, the prepared liquid sample S1 is irradiated with ultraviolet rays by means of the ultraviolet ray lamp 42 for approximately 20 minutes so that the nitrogen compounds are oxidatively decomposed into nitrate ions, and at the same time, potassium peroxydisulfate in the liquid is decomposed into potassium sulfate. After potassium peroxydisulfate has been entirely decomposed, a prepared liquid sample S1 is further irradiated with ultraviolet rays for 5 to 20 minutes so that nitrate ions are reduced into nitrite ions. After the completion of these reactions, the computer 160 outputs a drive signal to the pulse motor 12c, and thereby a predetermined amount (a+b+c+d) of the reacted liquid sample S2 is weighed and collected by the syringe pump 12. A drive signal is again outputted to the pulse motor 12c, and thereby a predetermined amount (e) of hydrochloric acid in the container 8 is added into the syringe 12a so as to generate a predetermined amount (a+b+c+d+e) of the prepared liquid sample S3.
Next, the computer 160 outputs a drive signal to the pulse motor 12c, and thereby the predetermined amount (a+b+c+d+e) of the prepared liquid sample S3 is introduced from the syringe pump 12 to the measuring cell 53. After that, a laser beam is emitted from the semiconductor laser element 51, and the light intensity I is detected by the photodiode 52. In addition, the computer 160 measures the absorbance at 220 nm on the basis of the detected light intensity I, and thus calculates the total nitrogen concentration in the prepared liquid sample S3.
3. Citation List